The engine test runs demonstrated that there were anomalies in the engine controls, specifically the engine rpm governors and the TCU. No other anomalies were found, so this analysis is limited to the engine controls. Because the acceleration and oscillation problems did not appear on the subject governors when the control arms were rigged in the normal range of 85 to 90, it was concluded that the rigging, prompted by a non-standard TCU, affected the operation of the governors. However, it is recognized that the Nf governors operated for about 150hours before the engine power delivery problem and accident. This may be explained by the different control arm position elevating the effect of normal deterioration of the governors. The coincidence of the subject governors malfunctioning at the same time, despite their independence, may be explained by their equal time in service. Also, the fact that the substitute governors appeared to operate normally when they were run independently, and that they oscillated when the engines were run-up together, indicate rpm and torque oscillations on each engine may have aggravated the other governor's weaknesses due to wear. Since both engines drive a common transmission, oscillations in one engine would demand the other engine to try and compensate.Analysis The engine test runs demonstrated that there were anomalies in the engine controls, specifically the engine rpm governors and the TCU. No other anomalies were found, so this analysis is limited to the engine controls. Because the acceleration and oscillation problems did not appear on the subject governors when the control arms were rigged in the normal range of 85 to 90, it was concluded that the rigging, prompted by a non-standard TCU, affected the operation of the governors. However, it is recognized that the Nf governors operated for about 150hours before the engine power delivery problem and accident. This may be explained by the different control arm position elevating the effect of normal deterioration of the governors. The coincidence of the subject governors malfunctioning at the same time, despite their independence, may be explained by their equal time in service. Also, the fact that the substitute governors appeared to operate normally when they were run independently, and that they oscillated when the engines were run-up together, indicate rpm and torque oscillations on each engine may have aggravated the other governor's weaknesses due to wear. Since both engines drive a common transmission, oscillations in one engine would demand the other engine to try and compensate. The installation of a non-standard TCU required that the engine Nf governors be rigged abnormally. The non-approved rigging amplified the effect of normal-type wear in the governors; the governors did not function properly, resulting in inadequate power from both engines upon pilot demand. Rpm and torque oscillations probably aggravated the opposing engine rpm governors' weaknesses due to wear and caused malfunctions at the same time. The loss of power in both engines occurred at a critical time of flight, resulting in a hard landing.Findings as to Causes and Contributing Factors The installation of a non-standard TCU required that the engine Nf governors be rigged abnormally. The non-approved rigging amplified the effect of normal-type wear in the governors; the governors did not function properly, resulting in inadequate power from both engines upon pilot demand. Rpm and torque oscillations probably aggravated the opposing engine rpm governors' weaknesses due to wear and caused malfunctions at the same time. The loss of power in both engines occurred at a critical time of flight, resulting in a hard landing. In-service wear causes the governors to malfunction before reaching their overhaul life of 4500hours; the average time in service before they are removed for repair is about 1600hours.Finding as to Risk In-service wear causes the governors to malfunction before reaching their overhaul life of 4500hours; the average time in service before they are removed for repair is about 1600hours. On 22 April 2005, Aviation Safety Advisory A050009-1, Dual Engine Power loss - Power Turbine Governor Malfunctions, was sent to Transport Canada and copied to Pratt Whitney Canada, Honeywell and Rolls-Royce. The letter identified the aforementioned findings and noted that PT governors used in similar applications have shown premature wear, with many being removed from service because of fluctuating torque. The advisory suggests that the current approved TBO for these governors is too long, and that Transport Canada, in cooperation with Honeywell, Pratt Whitney Canada and Rolls-Royce, may wish to review the TBOs approved for these governors. Transport Canada responded to the advisory on 21 July 2005, indicating that a review of Service Difficulty Reports on Honeywell Nf governors as installed in Rolls-Royce 250 C20, PWC PT6T engines, does not indicate a chronic problem with the time between overhauls. On 22 April 2005, Aviation Safety Advisory A050010-1, Dual Engine Power Loss - Power Turbine Governor Rigging, was sent to Pratt Whitney Canada and copied to Transport Canada and Honeywell. This letter also identified the aforementioned findings and noted that although the accident governors operated with the control arms at 74 and 73 for about 150hours before the power losses, it is apparent that the engine oscillation and acceleration problems were present only when the governor control arms were rigged in the 75 range. The advisory suggests that because power turbine governors are essential engine controls, which can cause critical power losses when they malfunction, Pratt Whitney Canada, in cooperation with Honeywell, may wish to review the effects of having to rig the PT6 power turbine governor control arms in the 75 range. Transport Canada responded to the advisory on 21 July 2005, indicating that the Department would not be taking any action regarding the advisory pending new information indicating aircraft certification concerns.Safety Action On 22 April 2005, Aviation Safety Advisory A050009-1, Dual Engine Power loss - Power Turbine Governor Malfunctions, was sent to Transport Canada and copied to Pratt Whitney Canada, Honeywell and Rolls-Royce. The letter identified the aforementioned findings and noted that PT governors used in similar applications have shown premature wear, with many being removed from service because of fluctuating torque. The advisory suggests that the current approved TBO for these governors is too long, and that Transport Canada, in cooperation with Honeywell, Pratt Whitney Canada and Rolls-Royce, may wish to review the TBOs approved for these governors. Transport Canada responded to the advisory on 21 July 2005, indicating that a review of Service Difficulty Reports on Honeywell Nf governors as installed in Rolls-Royce 250 C20, PWC PT6T engines, does not indicate a chronic problem with the time between overhauls. On 22 April 2005, Aviation Safety Advisory A050010-1, Dual Engine Power Loss - Power Turbine Governor Rigging, was sent to Pratt Whitney Canada and copied to Transport Canada and Honeywell. This letter also identified the aforementioned findings and noted that although the accident governors operated with the control arms at 74 and 73 for about 150hours before the power losses, it is apparent that the engine oscillation and acceleration problems were present only when the governor control arms were rigged in the 75 range. The advisory suggests that because power turbine governors are essential engine controls, which can cause critical power losses when they malfunction, Pratt Whitney Canada, in cooperation with Honeywell, may wish to review the effects of having to rig the PT6 power turbine governor control arms in the 75 range. Transport Canada responded to the advisory on 21 July 2005, indicating that the Department would not be taking any action regarding the advisory pending new information indicating aircraft certification concerns.